A number of systems are known in the prior art which are capable of compacting soil during construction of automobile roads, railroads, airfields, etc. The proper compaction of the soil base is intended to ensure that the mentioned constructions will reliably withstand loads of various kinds, including non-uniform, non-periodic and extremely high surface pressures. Methods and systems for evaluating soil compaction are also known, but generally, they are only capable of evaluating the compaction of an uppermost layer in a soil base. Further, even for the uppermost layer in a soil base, these methods are not capable of deriving both the compaction and the thickness of the single layer. Where these methods and systems work with compaction machines, they also cannot control the depth at which the compaction will take place.
U.S. Pat. No. 5,426,972 describes a method and an apparatus for determining whether soil is satisfactorily compacted. An operator delivers impact energy to the soil, and the amount of impact energy transmitted through the soil is repeatedly sensed and stored. A modeling formula, which approximates the variation of the stored amounts of impact energy, is used to generate current and target values for the level of compaction; if the current value equals or exceeds the target value, the soil is considered to be satisfactorily compacted. The target value is considered to be one common parameter of the soil regardless whether it comprises many different layers.
SU 717623 teaches a method of controlling the degree of compaction of soil embankments by transmitting into the embankment a vibratory signal with an adjustable frequency close to its calculated resonant frequency and estimating the compaction degree based on the real resonant frequency of the soil.
Commercially available modern systems for soil compaction are manufactured by a widely known German company BOMAG and a Swedish company GEODYNAMIK and are adapted for continuously measuring in situ the degree of compaction of a layer currently undergoing treatment, namely detecting the condition of the upper layer of the construction. Such systems are suitable for successively (i.e. layer by layer) forming the multi-layered base for a road or the like.
However, if any multi-layered base already exists, no means for examining the compaction degree thereof are available in these systems. It should be emphasized that constructing a road or the like on a non-explored and/or improperly compacted base is likely to result in serious problems during further use of the road.
An approach to the compaction of existing multi-layered soils is suggested in SU 763506, which is incorporated herein by reference. According to the approach described therein, different layers of any existing soil base which are exposed to vibrations created by any particular compaction instrument, can be represented as a number of differential equations reflecting free oscillation of a mechanical system disposed between the compaction instrument and the immovable bottom of the base, wherein each of the equations has its own static and dynamic parameters reflecting the layer's characteristics. The method suggests generating and solving a system of equations for a particular multi-layer base, for determining resonant frequencies of different layers of the base, and further performing the compaction of the base using the minimal resonant frequency which has been determined for the system, thus obtaining the maximal deformation and compaction of the soil.
However, it has been found and proven by the inventor that compacting each and every layer of the base maximally may not always produce optimal compaction results.